The present invention relates to an optical recording and reproducing apparatus which records optical information on a optical disk and reproduces the optical information therefrom by the use of an optical beam, and more particularly, to an apparatus and a method for reproducing information out of an optical recording disk. The optical disk is typically a magneto-optical medium and the information comprised data or audio/video information.
An optical recording/reproducing apparatus of this type is extensively used today because of its advantages that no physical contact is needed between an optical head for emitting a light beam and a n optical disk in recording/reproducing operations, and random access is permitted. In recording, a light beam modulated by information strikes a disk to record it in the form of pits on a track of the disk, while the recorded information is reproduced by directing a light beam to the track and sensing the variation in the intensity of a reflection.
An optical recording and reproducing apparatus of the type described is apt to suffer from crosstalk from neighboring tracks and intersymbol interference from neighboring pits on the same track during playback mode operation. Specifically, when the spot of a light beam illuminating a track is enlarged to extend over to neighboring tracks or when the center of the spot is not coincident with that of a track, crosstalk occurs. When the spot of a light beam is enlarged to illuminate neighboring pits on the same track simultaneously, intersymbol interference occurs. These problems are more serious in the event of high-density recording wherein the distance between nearby tracks and the distance between nearby pits are extremely short.
An implementation for eliminating crosstalk from neighboring tracks is disclosed in Japanese Patent Laid-Open Publication No. 61-287056. This implementation is such that pilot signals each having a different frequency are recorded on respective tracks, e.g., three tracks, beforehand. Crosstalk amounts for neighboring tracks are determined by sensing a reflection of a light beam from a desired track and the neighboring tracks. Components of the pilot signals assigned to the neighboring tracks and contained in the reflection represent the crosstalk amounts. In playback operation, three light beams are directed respectively to the desired and neighboring tracks and three optical sensors including a main sensor sense respective reflections of the light beams from the tracks to reproduce respective signals. The signals from the sensors corresponding to the tracks neighboring the desired track are controlled to produce reference levels corresponding to the amounts of crosstalk. Then, the signal from the main sensor for the desired track is processed, to produce a crosstalk-compensated reproduced signal by subtracting the reference levels from the signal from the main sensor. A problem with this prior art is that this crosstalk compensation is vulnerable to the displacement in location of light beam spots on the tracks and the fluctuation in size of the beam spots. Further, the prior art requires a more complicated structure since the pilot signal having a frequency different from that of a recorded signal should be interposed.